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''Shigella'' is a
genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circumscribing) and classifying gr ...
of
bacteria Bacteria (; common noun bacteria, singular bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typ ...

bacteria
that is
Gram-negative Gram-negative bacteria are bacteria Bacteria (; common noun bacteria, singular bacterium) are a type of Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few microm ...
, facultative anaerobic, non-spore-forming, nonmotile,
rod-shaped A bacillus (plural bacilli), or bacilliform bacterium, is a rod-shaped bacterium Bacteria (; common noun bacteria, singular bacterium) are a type of Cell (biology), biological cell. They constitute a large domain (biology), domain of prok ...
and genetically closely related to ''
E. coli
E. coli
''. The genus is named after
Kiyoshi Shiga was a Japanese physician A physician (American English), medical practitioner (English in the Commonwealth of Nations, Commonwealth English), medical doctor, or simply doctor, is a professional who practices medicine, which is concerned with ...

Kiyoshi Shiga
, who first discovered it in 1897. The causative agent of human
shigellosis Shigellosis is an infection of the intestines The gastrointestinal tract, (GI tract, GIT, digestive tract, digestion tract, alimentary canal) is the tract from the mouth to the anus which includes all the organ (anatomy), organs of the digest ...
, ''Shigella'' causes disease in
primate A primate ( ) (from Latin , from 'prime, first rank') is a eutherian mammal constituting the Taxonomy (biology), taxonomic order (biology), order Primates (). Primates arose 85–55 million years ago first from small Terrestrial animal, ...

primate
s, but not in other mammals. It is only naturally found in humans and gorillas. During infection, it typically causes
dysentery Dysentery () is a type of gastroenteritis Gastroenteritis, also known as infectious diarrhea and gastro, is inflammation of the gastrointestinal tract The gastrointestinal tract, (GI tract, GIT, digestive tract, digestion tract, aliment ...
. ''Shigella'' is one of the leading bacterial causes of
diarrhea Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery defecation, bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration of ...
worldwide, causing an estimated 80–165 million cases. The number of deaths it causes each year is estimated at between 74,000 and 600,000. It is one of the top four pathogens that cause moderate-to-severe diarrhea in African and South Asian children.


Classification

''Shigella'' species are classified by three and one
serotype A serotype or serovar is a distinct variation within a species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often d ...

serotype
: * Serogroup ''A'': '' S. dysenteriae'' (15 serotypes) * Serogroup ''B'': '' S. flexneri'' (9 serotypes) * Serogroup ''C'': '' S. boydii'' (19 serotypes) * Serogroup ''D'': '' S. sonnei'' (one serotype) Groups ''A''–''C'' are physiologically similar; ''S. sonnei'' (group ''D'') can be differentiated on the basis of biochemical metabolism assays. Three ''Shigella'' groups are the major disease-causing species: ''S. flexneri'' is the most frequently isolated species worldwide, and accounts for 60% of cases in the developing world; ''S. sonnei'' causes 77% of cases in the developed world, compared to only 15% of cases in the developing world; and ''S. dysenteriae'' is usually the cause of epidemics of dysentery, particularly in confined populations such as refugee camps. Each of the ''Shigella'' genomes includes a virulence
plasmid A plasmid is a small, extrachromosomal DNA Extrachromosomal DNA (abbreviated ecDNA) is any DNA that is found off the chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. Most eukaryo ...
that encodes conserved primary virulence determinants. The ''Shigella''
chromosome A chromosome is a long DNA molecule with part or all of the genome, genetic material of an organism. Most eukaryotic chromosomes include packaging proteins called histones which, aided by Chaperone (protein), chaperone proteins, bind to and ...

chromosome
s share most of their genes with those of ''E. coli'' K12 strain MG1655.
Phylogenetic In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanism ...

Phylogenetic
studies indicate ''Shigella'' is more appropriately treated as
subgenus In biology, a subgenus (plural: subgenera) is a taxonomic rank directly below genus. In the International Code of Zoological Nomenclature, a subgeneric name can be used independently or included in a binomen, species name, in parentheses, placed ...
of ''
Escherichia ''Escherichia'' is a genus of Gram-negative, non-Endospore, spore-forming, Facultative anaerobic organism, facultatively anaerobic, rod-shaped bacteria from the family Enterobacteriaceae. In those species which are inhabitants of the gastrointest ...
'', and that certain strains generally considered ''E. coli''—such as ''E. coli'' O157:H7—are better placed in ''Shigella'' (see '''' for details).


Pathogenesis

''Shigella'' infection is typically by
ingestion Ingestion is the consumption of a substance by an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classifie ...
. Depending on the health of the host, fewer than 100 bacterial cells can be enough to cause an infection. ''Shigella'' species generally invade the
epithelial Epithelium is one of the four basic types of animal Tissue (biology), tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed Cell (biology), cells with little Ext ...
lining of the
colon Colon commonly refers to: * Colon (punctuation) (:), a punctuation mark * Major part of large intestine, the final section of the digestive system Colon may also refer to: Places * Colon, Michigan, US * Colon, Nebraska, US * Kowloon, Hong Kong, s ...

colon
, causing severe inflammation and death of the cells lining the colon. This inflammation results in the diarrhea and even
dysentery Dysentery () is a type of gastroenteritis Gastroenteritis, also known as infectious diarrhea and gastro, is inflammation of the gastrointestinal tract The gastrointestinal tract, (GI tract, GIT, digestive tract, digestion tract, aliment ...
that are the hallmarks of ''Shigella'' infection. Some strains of ''Shigella'' produce toxins which contribute to disease during infection. ''S. flexneri'' strains produce ShET1 and ShET2, which may contribute to diarrhea. ''S. dysenteriae'' strains produce
Shiga toxin Shiga toxins are a family of related toxins with two major groups, Stx1 and Stx2, expressed by genes considered to be part of the genome In the fields of molecular biology and genetics Genetics is a branch of biology concerned ...
, which is hemolytic similar to the
verotoxin Shiga toxins are a family of related exotoxin, toxins with two major groups, Stx1 and Stx2, expressed by genes considered to be part of the genome of Lambdavirus, lambdoid prophages. The toxins are named after Kiyoshi Shiga, who first describ ...
produced by enterohemorrhagic ''E. coli''. Both Shiga toxin and verotoxin are associated with causing potentially fatal hemolytic-uremic syndrome. ''Shigella'' species invade the host through the
M-cells Microfold cells (or M cells) are found in the gut-associated lymphoid tissue (GALT) of the Peyer's patches in the small intestine, and in the mucosa-associated lymphoid tissue (MALT) of other parts of the human gastrointestinal tract, gastrointesti ...
interspersed in the gut epithelia of the
small intestine The small intestine or small bowel is an organ (anatomy), organ in the human gastrointestinal tract, gastrointestinal tract where most of the #Absorption, absorption of nutrients from food takes place. It lies between the stomach and large intes ...

small intestine
, as they do not interact with the apical surface of epithelial cells, preferring the basolateral side. ''Shigella'' uses a type-III secretion system, which acts as a biological syringe to translocate toxic effector proteins to the target human cell. The effector proteins can alter the metabolism of the target cell, for instance leading to the
lysis Lysis ( ; Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 1 ...
of
vacuolar A vacuole () is a membrane-bound organelle In cell biology, an organelle is a specialized subunit, usually within a cell (biology), cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts ...
membranes or reorganization of actin polymerization to facilitate intracellular motility of ''Shigella'' bacteria inside the host cell. For instance, the IcsA effector (which is an autotransporter instead of type III secretion system effector) protein triggers actin reorganization by N-WASP recruitment of
Arp2/3 complex Arp2/3 complex (Actin Related Protein 2/3 complex) is a seven-subunit protein complex that plays a major role in the regulation of the actin cytoskeleton. It is a major component of the microfilament, actin cytoskeleton and is found in most actin ...
es, helping cell-to-cell spread. After infection, ''Shigella'' cells multiply intracellularly and spread to neighboring epithelial cells, resulting in tissue destruction and characteristic
pathology Pathology is the study of the causesCauses, or causality, is the relationship between one event and another. It may also refer to: * Causes (band), an indie band based in the Netherlands * Causes (company), an online company See also * Cau ...
of shigellosis.The most common symptoms are
diarrhea Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery defecation, bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration of ...
,
fever Fever, also referred to as pyrexia, is defined as having a temperature Temperature ( ) is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy Thermal radiation in visible light can be seen on th ...

fever
,
nausea Nausea is a diffuse sensation of unease and discomfort, often perceived as an urge to vomiting, vomit. While not painful, it can be a debilitating symptom if prolonged and has been described as placing discomfort on the chest, upper abdomen, or ...

nausea
,
vomiting Vomiting (also known as emesis and throwing up) is the involuntary, forceful expulsion of the contents of one's stomach The stomach is a muscular, in the of humans and many other animals, including several s. The stomach has a dilat ...

vomiting
, stomach cramps, and
flatulence Flatulence is defined in the medical literature as "flatus expelled through the anus" or the "quality or state of being flatulent", which is defined in turn as "marked by or affected with gases generated in the intestine or stomach; likely to ...
. It is also commonly known to cause large and painful bowel movements. The stool may contain blood, mucus, or pus. Hence, ''Shigella'' cells may cause dysentery. In rare cases, young children may have
seizures An epileptic seizure, formally known as a seizure, is a period of symptom Signs and symptoms are the observed or detectable signs, and experienced symptoms of an illness, injury, or condition. A sign for example may be a higher or lower tem ...
. Symptoms can take as long as a week to appear, but most often begin two to four days after ingestion. Symptoms usually last for several days, but can last for weeks. ''Shigella'' is implicated as one of the pathogenic causes of
reactive arthritis Reactive arthritis, formerly known as Reiter's syndrome, is a form of inflammatory Inflammatory may refer to: * Inflammation, a biological response to harmful stimuli * The word ''inflammatory'' is also used to refer literally to fire and flammabil ...
worldwide.


Discovery

The genus Shigella is named after Japanese physician
Kiyoshi Shiga was a Japanese physician A physician (American English), medical practitioner (English in the Commonwealth of Nations, Commonwealth English), medical doctor, or simply doctor, is a professional who practices medicine, which is concerned with ...

Kiyoshi Shiga
, who researched the cause of dysentery. Shiga entered the Tokyo Imperial University School of Medicine in 1892, during which he attended a lecture by Dr. Shibasaburo Kitasato. Shiga was impressed by Dr. Kitasato's intellect and confidence, so after graduating, he went to work for him as a research assistant at Institute for Infectious Diseases. In 1897, Shiga focused his efforts on what the Japanese referred to as a "Sekiri" (dysentery) outbreak. These epidemics were detrimental to the Japanese people and occurred often in the late 19th century. The 1897 ''sekiri'' epidemic affected >91,000, with a mortality rate of >20%. Shiga studied 32 dysentery patients and used
Koch's Postulates 200px, Robert Hermann Koch (11 December 1843 – 27 May 1910) was a German physician who developed Koch's postulates. Koch's postulates ()
to successfully isolate and identify the bacterium causing the disease. He continued to study and characterize the bacterium, identifying its methods of toxin production i.e
Shiga Toxin Shiga toxins are a family of related toxins with two major groups, Stx1 and Stx2, expressed by genes considered to be part of the genome In the fields of molecular biology and genetics Genetics is a branch of biology concerned ...
, and worked tirelessly to create a vaccine for the disease.


See also

* Apocholate citrate agar *
Diarrhea Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery defecation, bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration of ...
* Enterotoxigenic ''E. coli'' *
Gastroenteritis Gastroenteritis, also known as infectious diarrhea and gastro, is inflammation of the gastrointestinal tract The gastrointestinal tract, (GI tract, GIT, digestive tract, digestion tract, alimentary canal) is the tract from the mouth to the ...

Gastroenteritis
*
Traveler's diarrhea Travelers' diarrhea (TD) is a stomach and intestinal infection. TD is defined as the passage of unformed stool (one or more by some definitions, three or more by others) while traveling. It may be accompanied by abdominal cramps, nausea, fever, a ...

Traveler's diarrhea


References


External links


Shigella
genomes and related information a
PATRIC
a Bioinformatics Resource Center funded b
NIAID

Vaccine Resource Library: Shigellosis and enterotoxigenic ''Escherichia coli'' (ETEC)

US Centers for Disease Control and Prevention. ''Shigella'' - Shigellosis
{{Taxonbar, from=Q131029 Enterobacteriaceae Neglected tropical diseases Tropical diseases Waterborne diseases Biological weapons Gram-negative bacteria Bacteria genera